Category: Preamps
This is not necessarily a review of the Callisto Signature itself (that has already been done), but rather relates to some new tube rolling options I have recently discovered. More specifically, the KT-66 tube as a replacement to the EL-34 that typically is used in the unit.
To start I listen to all kinds of music, from Rock and Blues, to jazz, County (early), singer song writer, Bluegrass, some Classical, and Rap/Hip Hop. I really enjoy a variety of recordings too, from early field recordings of Muddy Waters, to purist audiophile stuff like Analogue Productions (the new 45 rpm Jazz series is great, BTW). I am mainly an analog guy and will go out of my way to puchase a record if I can (over the CD version)...... It's fair to say that I have listened to all of these kinds of recordings during my time with this preamp.
I place an emphisis on musicality, resolution (not necessarily detail), and most of all tonality. The other audiophile stuff, like soundstaging and PRAT are certainly factors but come in on down the list. You can check out the link to "My system"......... I'm into tubes and have just found my way to SET amps and horns after a love affair with Electrostats and big tubes (Martin Logan Prodigy's and ARC VT200 for anyone wondering).
I bought the Aesthetix Callisto Signature preamp to replace my ARC LS25II some months back. It has been a major sonic upgrade for me. A couple of months ago my (obsessive) curiosity got the best of me and I figured I would try some tube rolling in the unit. Background: I am a professional musician/guitar player and own (have owned) quite a few vintage amps.......... Well, I had some NOS tubes around from an old VOX AC30 and from a '59 Fender Twin so I figured what the heck. First I put in a pair of Amperex EL-34 Bugle Boy's (probably mid '60's vintage)... the sound took a huge leap forward in liquidity and smoothness. I had more resolution, a lot better bottom end and the high's were much "prettier". In essence everything got a little bit better.........
I guess I couldn't leave well enough alone. I have a quartet of NOS Genelex KT-66's from the Fender that I have been saving to put in my portfolio for when the kids need that education. They are not a direct replacement (and I'm not a tube expert) but I have heard of people swapping them in their guitar amps, etc. I emailed Jim White and got his opinion...... He said he had never tried it but has had some customers who swear by the substitution. At this point I figured I was on to something interesting.....
When I put the KT-66's in everything went up another notch...... Maybe three or four notches actually. Everything I heard with the Bugle Boy's was multiplied. The biggest differences though were in the bottom end extension. Thunderous bass, tight and big. It sounded like I had installed a sub woofer. The highs are very sweet and extended........ And the mids are just creamy and dreamy. These tubes are a bit quieter too. I don't know if this is inherent or just my samples.
After all of this, I took Albert Porter and Jfox's advice on further tube substitutions..... I am now using Mullard gold pin 6922's, RCA 5692 (6SN7's), Tele 12AX7's.... These substitutions have made a great sonic impact as well, taking the amp to yet another level of performance.
This thread is about the KT-66 though..... I recently put the Bugle Boy's back in for a reference after the other tube swaps. No comparison, the KT-66's are a huge improvement for me. All as mentioned above but maybe even magnified with the NOS tubes.......
So, for you fellow Callisto owners, if you want to try an interesting experiment you may like what you hear.
Caveats: Per Jim White: "I have friends that have successfully substituted KT66s. I don't generally void the warranty unless the substituted tube causes the failure, which I can nearly always determine by the failure. We have had few cases like that in over 10 years of production"...... I have been running them for about three months with no problems. One more thing, becouse they are a lot bigger than the EL-34's the cover will not fit on the pre either.
Anyway, I hope this might provide us with some discussion and other interesting findings in reference to this great preamp.
Chris
Associated gear Click to view my Virtual System
